The present disclosure relates to roller pumps used in medical devices or systems (e.g., heart-lung bypass machine). More particularly, it relates to roller pumps having occlusion adjustment features that can be actuated during operation of the pump.
Roller (or peristaltic) pumps have many uses in the medical field. For example, roller pumps are used during cardiovascular surgery to facilitate circulation of blood between a patient and a heart-lung machine. The operation of a roller pump is to pump fluid by positive displacement using revolving rollers that occlude flexible tubing. In the context of a heart-lung machine, several dedicated roller pumps are commonly used as part of the perfusion circuit to pump the arterial circuit (where a centrifugal pump is not used), vent, cardiotomy suction, and cardioplegia. Other common medical uses are the transfer of blood between a patient and a kidney dialyzer, and intravenous (IV) feeding of IV solutions. Generally, roller pumps are simply structured, generate a constant flow, and use disposable tubing through which a fluid medium is transferred.
Roller pumps generally comprise a pump drive and a pump head. The pump drive causes rotation of the pump head to pump a fluid medium. The pump head comprises a pump stator and a pump rotor. The pump stator is essentially a chamber or housing having an inner circumferential surface (or “raceway”) against which one or more tubes are compressed by the pump rotor. The pump rotor, which is rotatable relative to the stator, is arranged in the pump stator in such a manner that the pump rotor engages tubing positioned in the pump stator with one or more rollers. Upon rotation of the pump rotor by a rotating shaft that is otherwise part of the pump drive, the roller(s) compress the tubing against the inner circumferential surface of the pump stator as it is rolled along the tubing. The fluid medium contained in the tubing is then transported in a direction of the pump rotor rotation.
It is important that roller pumps be adjustable. One way that rotor pumps are generally adjustable is with respect to the rate of rotation of the rotor, including the rollers. Most roller pumps have controls that allow a user to adjust and/or set the rotation rate. Another way that roller pumps are generally adjustable is with respect to the distance between the rollers and the inner circumferential surface of the stator. This parameter is often referred to as “occlusion” and reflects the degree to which the tubing is compressed or occluded between the rollers and the raceway surface. The degree or level of occlusion increases as the rollers are moved into closer proximity with the raceway surface. Varying the amount the rollers occlude or compress the diameter of the tubing in the pump as they move affects the pumping rate. The level of occlusion of the tubing also affects the amount of suction on the fluid medium. If the roller pump is used in certain portions of the anatomy, there may be limits on the amount of suction that can be applied safely to withdraw a fluid medium. An example of such a use for a roller pump is connected to a heart vent line, where too much suction could result in tissue damage. Additionally, the distance between the rollers and the raceway may be adjusted to accommodate differentially-sized (or quality) tubing. In summary, a perfusionist often desires to adjust occlusion to optimize competing criteria such as blood hemolysis, tubing spatulation, flow rate calculation accuracy, and to compensate for manufacturing variations in tubing.
Conventional perfusion roller pumps typically incorporate an occlusion adjustment mechanism that allows the perfusionist to manually adjust the occlusion “setting” or level. Known occlusion adjustment mechanisms are relatively simplistic, and require that the pump drive be deactivated (i.e., the roller pump is not pumping fluid) while the occlusion setting is adjusted. While viable, this approach can be quite time consuming and requires that the pump be stopped every time the perfusionist wishes to adjust occlusion. Moreover, occlusion adjustment typically requires the perfusionist to adjust the distance between the rollers and the raceway with one hand while holding a piece of tubing filled with a column of liquid at a height of one meter above the pump head with the other hand and determine when the column of liquid is dropping at a rate of 2.5 centimeters per minute. This is both cumbersome and inconsistent.
In light of the above, a need exists for roller pumps, especially roller pumps used in perfusion circuits, providing improved occlusion adjustment features.